Material for electrophotographic purposes



nited States Patent Ofihce $151,505 Patented Dec. 15, 1964 As is known, electrophotographic material consists of a support upon which there is a photoelectrically conductive insulator coating containing a photosemiconductor compound. This coatingis provided, in the dark, with an electrostatic charge and light is then shone imagewise on the material, either via the master or by the episcopic method, whereupon a latent electrostatic image that corresponds to the master is produced on the photoelectrically conductive coating. This image is developed by being contacted for a brief time with a resin powder; a visible image is thus formed as a result of the adherence of the resin to the charged parts, The image is fixed by heating or by the action of solvent vapor so that the resin is securely anchored to the support.

As the photosemiconductor compounds, inorganic substances such as selenium, sulfur or zinc oxide have been used. Also, organic substances such as anthracene, anthraquinone and benzidine have been employed for this purpose.

The present invention relates to a material for electrophotographic purposes consisting of a support and a photoelectrically conductive insulator coating, the latter consisting of or containing one or more thiodiazoles of the general formula R1 NN NJQJ km.

in which R and R are hydrogen or straight or branched chain saturated hydrocarbon groups which in the longest carbon chain contain up to 6 carbon atoms.

, Exemplary alkyl groups are methyl, ethyl, propyl,

butyl, isobutyl, pentyl and dimethyl pentyl.

As the thiodiazoles of the present invention, the following may, for example, be used:

2- (4- dimethylamino-phenyl) -5-amino-thiodiazole-1,3 ,4, .2-(4-diethylamino phenyl) -5-amino-thiodiazole-1,3,4,

2- (4-ethyl-n-propylamino-phenyl) -5-amino-thiodiazole- (Formula 1) (Formula 2) a i (Formula 6) A number of the thiodiazole compounds may be applied to the supporting material or they may be used in association with other known photoelectrically conductive substances.

The compounds in question are excellently suited for the production of photoelectrically conductive insulator layers and because of the improved homogenous nature of layers incorporating these compounds, they are an improvement over the layers hitherto known. The compounds are, in general, colorless and have photosemiconductor properties of the most desirable type.

The following are examples of supports for the photoconductor layer: foils made of metals such as aluminum, zinc and copper; cellulose products, such as paper and cellulose hydrate; cellulose esters, e.g., cellulose acetate and cellulose butyrate; or of plastics such as polyolefins, e.g., polyethylene and polypropylene; polyvinyl compounds, e.g., polystyrene, polyvinyl chloride and polyvinylidene chloride; polyacrylic compounds e.g., polyacrylonitrile and i polyrnethacrylate; polyesters, e.g., polyterephthalic acid glycol esters; polyamides and polyurethanes. i v

If paper is used as a supporting material, it is advisable for this 'to be pretreated to prevent the penetration of coating solutions, e.g., with a solution of methyl cellulose or polyvinyl alcohol inwater, or a solution of an interpolymer of acrylic acid. methyl ester with acrylonitrile in a mixture of acetone and methyl ethyl ketone, or solutions of polyamides in aqueous alcohols or with aqueous dispersions of such substances. Also, foils with a laminated metal surface, e.g., aluminum, are very suitable for 7 :these purposes.

For the preparation of the electrophotographic material of the invention, the photoelectrically conductive thiodiazole compounds are advantageously dissolved in organic solvents such as benzene, acetone, methylene chloride, ethylene glycol monomethyl ether or mixtures of such solvents and the supporting material is coated therewith in the usual manner, e.g., by immersion, spraying, painting or roller application.

Further, it is often advantageous for the thiodiazoles to be used as the photoelectrically conductive coating in association with organic resins. The following are examples of resins of this type: balsam resin, colophony, shellac and synthetic resins suchas phenol resins modified with colophony and other resins with a high proportion of colophony, coumarone resins, indene resins and the substances covered by the collective term synthetic lacquer resins. As is shown, for example, in the Plastics Handbook by Saechtling-Zebrowski, 11th edition (1955), p. 212 et seq., these synthetic lacquer resins include the following: processed natural substances such as cellulose ethers, polymers such as vinyl polymers, e.g., polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl ether, and polyacrylic and polymethacrylic esters, as well as polystyrene, isobutylene, chlorinated rubber, polycondensates, e.g., polyesters, such as phthalate resins, alkyd resins, maleinate resins, maleic acid/colophony mixed esters of higher alcohols, phenolformaldehyde resins, particularly colophony-rnodified phenol-formaldehyde condensates, urea-formaldehyde resins, melamine-formaldehyde condensates, aldehyde resins, ketone resins, xylene-formaldehyde resins, polyamides, and polyurethanes. Also, phthalic acid esters, such as terephthalic and isophthalic acid ethylene glycol polyesters, and polyolefins, such as polyethylene of low molecular weight and polypropylene, may be used.

If the compoundsof the invention are used in association with the resins described above, the proportion of resin to photoconductor substance can vary within wide limits. Mixtures in which the proportion of resin to photoelectrically conductive substance is between 2:1 and 1:2 are preferable. Particularly favorable results can be obtained by the use of mixtures in which the proportions are about equal.

The solutions of the thiodiazoles of the invention, with or without resins, are applied to the supporting material in the usual way, e.g., by painting, roller application or spraying. They are then dried, whereupon a uniform, homogeneous, transparent and usually colorless photoelectrically conductive coating is formed. The light sensitivity of these photoconductor coatings is in the long wave ultra-violent region between about 3600 and 4200 A. With high pressure mercury vapor lamps, which emit a high proportion of ultra-violent radiation, good results can therefore be obtained with very short exposures.

By the addition of sensitizers, the special sensitivity of the photoelectrically conductive coatings can be moved further into the visible region so that good results can be obtained with short exposures, even in the visible region. Even very small additions, e.g., somewhat less than 0.01%, produce good effects. The quantity of Sensitizer added to the photoelectrically conductive layer generally, however, amounts to 0.0l-% by weight, preferably 0.1-3%. A larger quantity of sensitizer can be added, but in general does not bring any greater increase in sensitivity. Such sensitizers, which in the main are dyestulfs, are disclosed for example in Belgian Patent No. 558,078.

For the preparation of copies using the electrophotographic reproduction material of the invention, the photoelectrically conductive insulator coating is charged, e.g., by a corona discharge from a charging device maintained at 6000-7000 volts. The electrophotographic material is then exposed, either in contact with a master or by episcopic or diascopic projection of the master, whereupon an electrostatic image corresponding to the master is produced. This invisible image is developed by being contacted with a developer consisting of a carrier and a toner. As the carrier, the materials used may be fine glass balls, iron powder or fine plastic balls. The toner consists of a mixture of a resin and carbon black or of a pigmented resin with an average grain size of about 1 to 100p. The developer can also comprise a resin or pigment suspended in a dielectric liquid. The image made.visible in this way is fixed, for example, by heatingwith an infra-red radiator to about 100170 C., preferably 120-7150" C., or by treatment with solvent vapor, e.g., trichloroethyle ne, carbon tetrachloride or ethyl alcohol, or with steam. In this way, images are obtained which correspond to the master and which have good contrast.

After being fixed, the electrophotographic images obtained in this manner, can also be converted into printing plates if the supporting material, e.g., paper or metal, is wiped over with a solvent for the photoelectrically conductive layer, e.g., alcohol or acetic acid, then rinsed down with water and inked up in known manner with greasy ink. in this way, printing plates are obtained from which prints can be made in an offset machine.

If transparent supporting material is used, the electrophotographic images can be used as masters for further copying on any type of light sensitive sheets. The photoconductive compounds of the invention are superior in this respect also to the substances hitherto used, such as selenium and zinc oxide, since use of the latter results in cloudy coatings.

Images can be produced by the reflex process as well, if a translucent supporting material is used for the photoconductor coatings of the invention. The present electrophotographic material has the advantage that it can be charged either positively or negatively so that positive images can be obtained with one and the same coating and the same developer, both from negative and from positive masters, by reversal of the polarity.

For example, if the coating is given a negative charge and is then exposed with a positive master, the use of a developer containing a positively charged toner will pro duce positive images. The positively charged toner settles on the negatively charged parts not affected by the light.

If the coating is positively charged, positive copies can be prepared from negative masters, where the conditions are otherwise the same. The positive toner is in this case repelled by the positively charged parts unaffected by the light and settles on the discharged parts that have been affected by the light.

The preparation of the photoelectrically conductive compounds of the invention consists of treatment of the corresponding p-alkylamino benzoic acid and 2 moles of thiosemicarbazide with polyphosphoric acid at C. Polyphosphoric acid acts as a dehydrating agent which at the same time etfectsring closure;'the reaction takes about 2 hours. The reaction mixture is then poured over ice and made alkaline (pH 89) with sodium-hydroxide. The thiodiazole compounds then precipitate out, are filtered off, recrystallized and dried. Some examples of this preparation are given below:

2-(4-dimethylamino-phenyl)-5-aminothiodiazole 1,3,4,- corresponding to Formula 1 (melting point: 239-240 C.), is prepared from 37.4 parts by weight of 4 dirrlcthyl amino benzoic acid and 36.4 parts by weight of thioseirii carbazide, which are heated for two hours with 500'parts by volume of polyphosphoric acid at 120 C. After the mixture has cooled, it is poured over 5000 parts by weight of ice and made alkaline with 4000 parts by volume of 25% sodium hydroxide. Colorless crystals precipitate out which are recrystallized from ethyl alcohol.

2-(4-diethylamino-phenyl)-5-amino-thiodiazole 1,3,4,- corresponding to Formula 2 (melting point: 224226 C.), is prepared from 38.6 parts by weight of 4-diethylamino benzoic acid and 36.4 parts by weight of thiosemicarbazide, which are heated for two hours with 500 parts by volume of polyphosphoric acid, working up as above. The yield is 5060%.

2-(4 ethyl-11-propylamino-phenyl)-5-amino-thiodiazole- 1,3,4, corresponding to Formula 3 (melting point: 217- 218 C.), is prepared from 41.4 parts by weight of 4- ethyl-n-propylarnino benzoic acid and 36.4 parts by weight of thiosemicarbazide, which are heated for two hours with 5 00 parts by volume of polyphosphoric acid.

2-(4-di-n-propylamino-phenyl)-5 amino thiodiazole. 1,3,4, corresponding to Formula -4 (melting point: 228- 230" C.), is prepared from 44.2 parts by Weight of 4-di-npropylamino benzoic acid and 36.4 parts by weight of thiosemicarbazide, which are heated for two hours with I 500 parts by volumeof polyphosphoric acid. The yield. is 60-85%.

2-(4-monoethylamino-phenyl) 5 amino thio'diazole- 1,3,4, corresponding to Formula 5 (melting point: 196 198" C.), is prepared from 33 parts by weight of 4-monoethylamino benzoic acid and 36.4 parts by Weight of thiosemicarbazide, which are heated for two hours with 500 parts by volume of polyphosphoric acid to 120 C.

2-(4-1nono-n-propylamino-phenyl)-5 amino thiodiazole-1,3,4, corresponding to Formula 6 (melting point: 188-190 C.), is prepared from 35.8 parts by weight of 4-mono-n-propylamino benzoic acid and 36.4 parts by weight of thiosemicarbazide, which are heated for two hours to 120 C. in 5 parts by volume of polyphosphoric acid.

2- (4-mono-isoamylamino-phenyl) -5-amino-thiodiazole- 1,3,4, corresponding to Formula 7 (melting point: 178- 179 C.), is prepared from 41.4 parts by weight of 4- mono-isoamylamino benzoic acid and 36.4 parts by weight of thiosemicarbazide, which are heated for two hours to 120 C., in 500 parts by volume of polyphosphoric acid. The yield is 80-90% The invention will be further illustrated by reference to the following specific examples:

Example I 1 part by weight of 2-(4-diethylamino-phenyl)-5-aminothiodiazole-l,3,4 (corresponding to Formula 2) and 1.2 parts by weight of a polyindene resin with a softening temperature of 80 C., commercially available under the name Gebaganharz J/T80, are dissolved in 30 parts by weight of ethylene glycol monomethyl ether. To this solution, 0.002 part by weight of Crystal Violet in 0.5 part by volume of methanol is added. The solution is applied to paper, the surface of which has been treated to prevent the penetration of organic solvents, and dried. The paper thus coated is provided by means of a corona discharge, with a negative electric charge. It is then exposed with a positive master to a high pressure mercury lamp and dusted over in known manner with a developer consisting of a mixture of a carrier and a toner. As the carrier, glass balls, iron powder and other inorganic substances can be used. The toner consists of a resin-carbon black mixture or pigmented resins of a grain size of between 1 and 100a. An image corresponding to the master is formed, which is fixed by slight heating; it has good contrast.

If a transparent support is used for the above process, e.g., a cellulose acetate foil or transparent paper, the image electrophotographically produced can be used as a master for further copying on light sensitive sheets.

Example 11 1 part by weight of 2-(4-ethyl-n-propylamino-phenyl)- S-amino-thiodiazole-1,3,4 (corresponding to Formula 3), 1.5 parts by weight of'a ketone resin with a softening temperature of 7682 Cxand an acid number of 0 (commercially available under the name Kunstharz AP) and 0.005 part by weight of Brilliant Green are dissolved in 20 parts by volume of ethylene glycol monomethyl ether and the solution is applied to a paper to which aluminum is laminated. After evaporation of the solvent, a coating remains which adheres firmly to the aluminum surface.

After negative charging by means of a corona discharge, the paper is given a second exposure with a positive master to a 100 watt filament lamp at a distance of about 30 cm. Development is then accomplished with a developer as described in Example I and an image corresponding to themaster appears, which is fixed with trichloroethylene vapor.

Example III 2 parts by weight of 2-(4-mono-isoamyl-amino-phenyl)- S-amino-thiodiazole-l,3,4 (corresponding to Formula 7), 0.4 part by weight of 2-(4-diethylamino-phenyl)-5-aminothiodiazole-1,3,4 (corresponding to Formula 2) and 0.4 part by weight of 2-(4-di-n-propyl-amino-phenyl)-5-amino-thiodiazole-1,3,4 (corresponding to Formula 4) are dissolved in 40 parts by volume of ethylene glycol monoethyl ether and the solution is applied to a brushed aluminum foil. After evaporation of the solvent, a coating remains which adheres firmly to the surface of the foil. The further procedure described in Example I is followed and an image corresponding to the master is obtained on the aluminum foil, if, after powdering over with a developer as described in Example I, the material is fixed by heating.

The aluminum foil thus provided with an image can be converted into a printing plate if the image side of the aluminum foil is wiped over with alcohol, rinsed with water and inked up with greasy ink together with 1% phosphoric acid. A printing plate corresponding to the master is obtained. This can be set up in an offset machine and used for printing.

Example IV The procedure described in Example I is followed but, after the coating has dried, it is positively charged and then exposed with a positive master. As the developer, a pigmented resin-carbon black mixture and glass balls covered with resin are used. A positive copy is obtained.

Example V 1 part by weight of 2-(4-mono-isoamylamino-phenyl)- S-amino-thiodiazole-1,3,4 (corresponding to Formula 7), 3 parts by weight of 2-(4-ethyl-n-propylamino-phenyl)-5- amino-thiodiazole-1,3,4 (corresponding to Formula 3) and 5 parts by Weight of a phenol-formaldehyde resin with a softening point of 108-118" C.commercially available under the name Alnovol 429 K-and 0.008 part by weight of Rhodamine B extra, are dissolved in parts by volume of ethylene glycol monomethyl ether. A paper is coated with the solution thus obtained. On this paper direct images are produced by the electrophotographic process in the manner described in Example I. The coatings are highly light sensitive so that images can also be produced thereon episcopically from masters with printing on both sides.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An electrophotographic material comprising a conductive support having a photoelectrically conductive insulating layer thereon, the latter comprising a thiodiazole having the formula in which R and R are selected from the group coni 2. An electrophotographic material according to claim 1 in which the thiodiazole has the formula 3. An electrophotographic material according to claim 1 m which the thiodiazole has the formula 4. An electrophotographic material according to claim 1 in which the thiodiazole has the formula 7 5. An electrophotographic material according to claim 1 in which the thiodiazole has the formula 6. An electrophotographic material according to claim 1 in which the thiodiazole has the formula H s 7. An electrophotographic material according to claim 1 in which the thiodiazole has the formula Ca 'l H s 8. An electrophotographic material according to claim 1 in which the thiodiazole has the formula i-C 5H11 "'N in which'R and R are selected from the group consisting of hydrogen and straight and branched chain alkyl groups in which the longest carbon chain contains up to six carbon atoms.

12. A process according to claim 11 in which the thio- 'diazole has the formula NN 0H, ,N-Q-(h i-NH:

13. A process according to claim 11 in which the thiodiazole has the formula N i l-NH:

14. A proces's according to claim 11 in which the thiodiazole has the formula C 2115 NN 431 am. 3 1 S 15. A process according to claim 11 in which the thiodiazole has the formula 16. A process according to claim 11 in which the thiodiazole has the formula C 2110 NN 17. A process according to claim 11 in which the thiodiazole has the formula 18. A process according to claim 11 in which the thiodiazole has the formula NN N i am 19. A process according to claim 11 in which the insulating layer includes a resin.

20. A process according to claim 11 in which the insulating layer includes a dyestuff sensitizer.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,691 Carlson Oct. 6, 1942 3,037,861 Hoegl et a1. June 5, 1962 3,041,165 Slls et a1. June 26, 1962 3,066,023 Schlesinger Nov. 27, 1962 3,066,147 Carmack et a1 Nov. 27, 1962 3,069,430 Schellhammer et a1. Dec. 18, 1962 3,097,095 Klupfel et al. July 9, 1963 FOREIGN PATENTS 836,148 Great Britain June 1, 1960 1,067,440 Germany Oct. 22, 1959 

1. AN ELECTROPHOTOGRAPHIC MATERIAL COMPRISING A CONDUCTIVE SUPPORT HAVING A PHOTOELECTRICALLY CONDUCTIVE INSULATING LAYER THEREON, THE LATTER COMPRISING A THIODIAZOLE HAVING THE FORMULA 